Annual Report 2001 - 2002

Scientific Research

Monsoon and Tropical Climate (MONTCLIM)

Studies related to the physics and dynamics of monsoons, land-ocean-atmosphere coupled system and indigenous development of technology for atmospheric science applications are being supported under the Monsoon and Tropical Climate Programme. In order to study the effect of weather and climate in tropics, efforts are being made to improve parameterisation of land-ocean-atmospheric processes in the Atmospheric General Circulation Models. Agrometeorological studies related to crop-weather relationships are also being sponsored under MONTCLIM.

Atmospheric Process Modelling

Studies on the role of moist processes and orography in general circulation model simulation of the monsoons revealed that there is a threshold value for precipitable water below which there is little precipitation. Above this threshold, precipitation increases monotonically with precipitable water. Air-sea interactive processes over the tropical Indian Ocean in relation to summer monsoon were studied using satellite data. The study indicated that the mean annual cycle of evaporation over the southern Indian Ocean shows build up of moisture from March and reach maximum in June. Then it decreases substantially with the withdrawal of summer monsoon from the Indian sub-continent indicating significant role played by the southern Indian Ocean in the monsoon activity of the Indian sub-continent. Initiated studies on `Meso-scale systems over Indian region' and `Evolution of atmospheric boundary layer through land surface interactions'.

Atmospheric Chemistry

Natural wet lands of Orissa are found to be a major source contributing about 19 million Kg of methane per year to the national green house budget, based on actual measurements carried out over a period of four years (1997-2000) integrated over three different seasons. The fresh water wet lands having hydrophytes contribute much more methane than the saline or semi saline wet lands. Chilka Lake, the largest semi saline wet land is the major contributor to this budget. The contributing factors are poor water quality, high concentration of organic carbon in soil and depletion of oxygen at the soil surface. The impact of natural processes and anthropogenic activities on the atmospheric chemistry of Dakshina Kannada and on the quality of natural waters, is being studied. Fortnightly samples of atmospheric precipitation and ground water were collected from 12 locations in and around Mangalore (Karnataka). Measurements of physiochemical parameters and aerosols are in progress. Studies related to emission of nitrous oxide from soils under rice-wheat cropping system are in progress. Initial results indicate that the emissions of nitrous oxide from soils subjected to intermittent wetting and drying in rice were more than from soils that were saturated irrespective of the source of Nitrogen.

Agrometeorology

The initial scientific results obtained from the land-surface process experimental data were published as a special issue of the Journal of Agrometeorology. Validated a COTTAM (Cotton crop growth and yield simulation) model under Dharwar agroclimatic conditions and studied the variability in crop growth, development, water use and yield in cotton. Similar experiments are planned for Punjab conditions. Field experiments on crop-weather relationships in Soybean and Rice, are in progress. Initiated studies on soil-vegetation-atmosphere interactions. An Expert Committee has been constituted to prepare a status report on "Development of Agrometeorology in India". A Questionnaire was prepared and circulated to obtain necessary inputs for the above task.

Technology Development

Indigenous development of technology for Wind Profiler / Radio Acoustic Sounding System for continuous atmospheric monitoring is successfully completed. The system was installed at Pune and data validation experiments are in progress. An Acoustic Wind Profiler for remote atmospheric wind measurement at low levels is under development. A new project for developing boundary layer Radar technology is being evolved. Indian Climate Research Programme (ICRP)

Studies related to temporal and spatial variability of climate, Past Climate and Climate Change and relationships between climate and agriculture, are being coordinated under ICRP. A `National Information Facility for Climate Research' is being established for collating, compiling, archiving information on climate research and dissemination to users. The salient achievements under the programme are as follows:

Bay of Bengal Monsoon Experiment

A nationally coordinated multi institutional field experiment called "Bay of Bengal Monsoon Experiment (BOBMEX)" was organised during 1999 for better understanding of the Ocean-Atmosphere coupled system. Organised a national workshop to discuss the initial results of the BOBMEX. About 32 research papers were presented during the workshop, which was attended by over 90 scientists. The data generated through the experiment is being further analysed. The significant initial results are as follows:

Atmospheric Dynamics: During the BOBMEX filed phase (July-August 1999), several active and weak spells of convection occurred over the Bay, represent intra-seasonal oscillations in the north Bay of Bengal. The Convective Available Potential Energy of the surface air decreased following convection, and recovered in one to two days. Even though the local thermodynamic instability was comparable during different phases of the intra-seasonal oscillation, the monsoon systems formed only during the active phase. The sea air temperature and specific humidity difference are significantly smaller in the north Bay compared to that observed over the equatorial west Pacific Ocean. Surface heat budget shows that horizontal advection is important in the north Bay. When horizontal advection is not dominating, one dimensional heat balance can predict the evolution of water surface temperature. Daily variation in the mid-tropospheric thermodynamic parameters over the north Bay were found to be sensitive to the location of the vortex and the trough line with respect to the ships position. Good agreement between radiometer derived and satellite derived total ozone content. Observed a bi-modal aerosol size distribution with maximum concentration of particles at primary mode of 0.02 mm radius and secondary mode around 1.0mm radius particles of fairly high concentration. The pH of the rain water over the north Bay of Bengal indicate alkaline nature. The Dimethyl Sulphide indicated high variability in response to intense atmospheric convection.

Ocean dynamics: The thermohaline structure as well as its time-evolution during the BOBMEX filed phase was found to be different in the north and south Bay of Bengal. Coastal turbidity marked by low incidence of light transmission and an isolated offshore freshwater plume characterised with higher chlorophyll were observed off Paradip. The temporal variations in the north Bay indicated conspicuous arrival of freshwater plume causing a fall in sea surface salinity and shallow mixed layer depth. The variations in oceanographic parameters at the south central Bay of Bengal are mostly dominated by the remote forcing compared to the local forcing. This study indicates the intraseasonal oscillations of 20-30 days played a role in the evolution of the Bay of Bengal Monsoon. The variation in the sea surface anomaly patterns observed through remote sensing during the monsoon periods of 1998 and 1999 emphasised the existence of the intra-seasonal oscillation. This appeared to be related to the equatorial wave phenomenon and the ENSO events.

Air-Sea Interaction: The sea surface temperature (SST) showed little variation during the disturbed periods, whereas the air-temperature showed large variation. A drop in air temperature typically 2-3 oC was noted. Observed a marginal diurnal variation in SST (0.4o to 1.0o C) and weak inversion in temperature (0.3oC to 0.6oC). The SST and Cyclone heat potential are in phase, even on diurnal scale. The SST and SSS (sea surface salinity) decreased during rain events and increased in cloudy conditions. An effective oceanic layer has been identified and investigated its close association with the atmospheric convection and cyclogenesis over Bay of Bengal. There is a possibility of predicting the mixed layer depth variability to a large extent by incorporating other physical processes. A net oceanic heat loss was found during the active convection period. Higher values of marine boundary layer height were noticed in the active period and lower values during suppressed convection. Transportation of fluxes of sensitive and latent heat from the surface layer into the boundary layer was taking place during active convection whereas it was found to be negligible during suppressed convection. The cyclone heat potential was higher at north of 10°N where two tropical cyclones formed. The vertical profiles of specific humidity and virtual potential temperature showed north-south gradients above 750 hPa helping in organized convection in the study area.

Arabian Sea Monsoon Experiment

A multi institutional field experiment namely, Arabian Sea Monsoon Experiment (ARMEX), is being planned to execute in two phases during the years 2002 and 2003. The main aim of the experiment is to get more insight into the intricacies involved in the formation and development of the Off-shore vortex and the warm pool over the Arabian sea. The `Working Group on Ocean-Atmosphere Field Experiments' finalised the technical programme to carryout ARMEX-I during 2002. The Science and Implementation plans for the ARMEX have been prepared. ARMEX Data Management Plan is under preparation. About 10 new project proposals are under processing.

Climate Modelling

A research project for understanding and predicting monsoon variability and El-nino Southern Oscillation (ENSO) - Snow-Monsoon interactions is under progress. Initial results indicated that the impact of ENSO events on the Indian monsoon rainfall (IMR) is modulated by the decadal variability in monsoon rainfall. The relationship between Soviet snow depth and the IMR shows that winter-time snow depth over western (eastern) Eurasia is negatively (positively) related to the subsequent IMR. This configuration is an indication of a mid-latitude longwave pattern with an anomalous ridge (trough) over north Asia prior to a strong (weak) monsoon.

Study of convective boundary layer during the summer monsoon season over the Bay of Bengal is under progress. Development of an optimized atmospheric general circulation model for sensitivity studies on monsoon climate is at an advanced stage. The modified filtered orography with 2-D digital filter is being used in this model simulation for the first time. Studies related to interannual variability of intraseasonal oscillations and the seasonal mean monsoon are under progress. New projects initiated are (1) Interannual variability of surface moisture and energy fluxes, 2) Parameterisation of biosphere-atmosphere interactions in a state-of-the-art forecasting General Circulation Model (GCM) in the perspective of Indian Monsoon, 3) Heat sources over India during southwest monsoon season, 4) Atlas of spatial features of moisture regions and rainfall of India during 19th and 20th Centuries, and 5) Monsoon variability in relation to NAO and ENSO and its use for predicting monsoon rainfall over smaller spatial and temporal scale.

Climate-Chemistry Interactions

Initiated modelling studies to understand the impact of anthropogenic and natural activities on climate forcing. The development of a new chemical module with interactive dynamics and radiative processes for the troposphere is underway. A new chemical scheme has been proposed for the troposphere as an independent module for steady state conditions using matrix inversion method. Initiated studies on differential absorption LIDAR sensing of Ozone.

Climate and Agriculture

Established an `Agrometeorological Data Bank' for collecting, compiling and archiving various types of agrometeorological data being generated under various programmes of DST and Indian Council of Agricultural Research. A dynamic web page for the above Data Bank is being developed. Coordinated field experimental data available with the India Meteorological Department, Pune is being analysed to develop crop-weather relationship models. Initiated studies on micro-regional (district as unit) rainfall variability and its influence on crop production in the eastern UP and Bihar plains. A workshop on Animal-Climate relationships is being organised. Deep Continental Studies

Deep Continental Studies (DCS) Programme is aimed at greater understanding of the geodynamics of the earth and inter relationships of its three components-the crust, the mantle and the core. Insights into the deep structure of continents, their crust and mantle are the major focuses of the programme. Substantial amount of work have already been carried out around a few selected geotransects or study areas. The focus of the investigations during the last one year have been multi-disciplinary studies along South Indian shield, NW Himalayan geotransect (HIMPROBE), Son-Narmada Lineament etc. Highlights / achievements of the programme are as under :-

New Projects

The following new projects have been sanctioned during the year 2001 :

• A geophysical study of the lithosphere below southwest continental margin of India..
  
• Computation of regional and residual gravity anomalies of India:-
  preparation of the maps.
  
• Database Management Systems for Pre-Cambrian ore deposits of India: a Web ready GIS approach.
  
• Geology, Geochemistry, Evolution and Mineralization of the Narayanpet-Gadwal- Velligullu Schist Belt and sorrounding Granitoids.
  
• o Role of Plume-Arc interaction and evolution of late Archean Continental
  Crust with special reference to Chitradurga Scist Belt.

Ongoing activities

• Tectonics, P-T Constraints and timing of India-Asia Collision along NW-Himalayas" (HIMPROBE)

Recent studies have indicated that northward moving Indian Plate appears to have an initial impingement along the Indus Tsangpo Suture Zone (ITSZ) and the Shyok Suture Zone (SSZ), and has caused the closure of the Tethys Ocean in Late Cretaceous. As a consequence, Paleo-Mesozoic marine platform witnessed latest Cretaceous-Paleocene fluvio-lacustrine deposition and yielded microbiota of considerable significance, which may provide important constraints on the timing of India-Asia collision within the ITSZ.

Detailed P-T estimation using various geothermo-barometric calculations on "eclogites" of Tso Morari areareveal peak temperature of about 7500 C and 20.2 kb pressure to 4500 C and 4.5 kb for these rocks indicating a minimum depth of subduction of the Indian Plate to about 60 km and exhumation to a shallower level and isothermal decompression to 10 kb followed by isobaric cooling. Filed investigations within the Shyok Suture Zone (SSZ) reveal the presence of dismembered oceanic crust having peridotite, gabbro, basalt, chert and shale, being juxtaposed against the Ladakh Batholith in the southwest.
Magnetotelluric(MT) studies in Ladakh

Magnetotelluric studies were conducted over the Pang-Upshi-Tangtse-Phobrang and Leh-Panamik profiles in the frequency range of 1000-0.0005 Hz in the Ladakh-Karakoram mountains. The resistivity structure shows a predominantly high resistive crust (>1000 ohm-m). A vertical conductive feature was delineated on the south of Tso Morari Crystallines, and may coincide with the tectonic boundary with the overlying Tibetan Sedimentary Zone.

• Structural Evolution of the NW Himalayas with special reference to inversion tectonics.

Geological field, anisotropy of magnetic susceptibility, finite strain (using Rr /<1> technique), and model deformation studies reveal that the Kangra or Punjab re-entrant is a primary structure. The re-entrant is a combination of frontal and oblique ramp structures. The fault initiated as normal listric fault during an initial tensional phase prior to the Himalayan orogeny and later reactivated as thrust listric fault during the Himalayan orogeny. Balanced cross-sections from the western Himalayan foreland foothill belt reveal a variation in shortening amounts from 22% to 71.3% Over a lateral distance of -85km. The large variation may be attributed to the fact that the method of cross-section balancing considers the initial layering as horizontal, which is an unlikely situation in foreland basins. Simple trigonometric relationships are provided to minimize the error in shortening estimates. The study indicates that shortening rates for the area based on the present shortening estimates cannot be used for earthquake prediction.

Seismic Modeling of the Narmada - Son Region

The above mentioned study involved reinterpretation of the deep seismic refraction / wide-angle reflection data along the profiles recorded across this zone. Reinterpretation of this data led to the following conclusions:

• The Narmada zone is divided in two parts by the NW-SE trending Barwani-Sukta fault.
  
• Sedimentary graben under the Deccan Traps to the west of this fault exists, while to its east the zone is represented by a basement uplift.
  
• A 8.0 km thick high velocity / high density mafic intrusion has been
  interpreted in the eastern part. The intrusion activity is separated by a narrow zone of uplift between the Narmada north and south faults, where the mafic intrusion is only 2 - 3 km thick.
  
• The development of the Narmada zone appears to have taken place in at
  least 3 phases during Proterozoic, Gondwana and Deccan Trap extrusion during the late Cretaceous.
  
• Fractal studies for enhance detectibility of geophysical anomaly by optimal design of gravity/magnetic surveys in Jabera-Damoh, Vindhyan basin, M.P."

A preliminary interpretation of magnetic anomaly has been done using Werner deconvolution for basement mapping of the area. This method is based on the assumption that the source is vertical thin dike of uniform magnetization. Three profiles as marked on the magnetic anomaly map are interpreted using Werner deconvolution and a basement contour map has been prepared. Basement map shows gradually increasing depth of basement towards Jabera from Damoh. Several other profiles have been attempted for the interpretation but due to absence of reasonable anomaly in other parts this method could not be used for basement depth determination. Fractal and Scaling spectral analysis of gravity and magnetic data is in progress. Magnetic anomaly map of the area covered till date and basement contour map is shown in Fig.2 and Fig 3.respectively. Basement contour map is obtained from the results of Werner deconvolution along three profiles shown in magnetic anomaly map.

Modelling the tectonic evolution of Southern Granulite Belt of the Indian Shield using different geophysical methods.

The integrated geophysical experiment using seismic, gravity, magnetotellurics and deep resistivity sounding to evaluate the deep crustal configuration of the southern granulite belt, has yielded very useful information regarding velocity, density and conductivity of the upper, middle, and lower crustal columns thereby bring into focus the varied composition of different crustal layers. A better understanding of the southern granulite belt has been achieved by the synthesis of geophysical, geological and geochemical studies. The study has brought out local and regional tectonic/structural variations emphasizing the complicated nature of the southern granulite terrain due to the influence of mega shear zones and lateral and vertical composition variations present in the upper, middle and lower crustal column.

Broad Band Seismic Experiments in South India

To investigate the seismic properties of the crust and upper mantle of geological terrains of South India, an experiment is currently in progress. The methodology employs broadband recording of earthquake waveforms at various locations and numerical simulation to arrive at P and S wave velocity, S wave anisotropy and Poisson's ratio. Most significant results from this study includes:

• A remarkably uniform crust of the eastern Dharwar craton with 35 +1- 2 km average thickness, 3.73 +1- 0.10 Km/s average shear wave velocity and 0.25 Poisson's ratio.
  
• Significant thickening of the crust underneath the mid- Archean segment of western Dharwar craton. The crustal thickness is inferred to be ~ 47 +1-2 km. This is the first global reporting of anomalously thick and quartz rich mid -Archean crust.
  
• Travel time residual analysis show seismically high velocity thick lithosphere beneath Dharwar craton compared to thin lithosphere beneath the Southern Granulite Terrain.

Further modelling work is in progress to study 3-D velocity structure, 3-D mantle layering and anisotropy in lithosphere. These results would help us in building mechanism for the crustal evolution in South Indian and its possible similarity or variance with the global models.

Integrated geological and geochemical investigation of the Gadag-Dharwar-Panaji sector of Karnatak Craton.

It has been reported that there is a presence of marine platformal sequence, comprising of iron oxide-ankerite bearing cherts and minor carbonaceous phyllites in association with mafic-ultramafic flows (the latter included a pillow lava horizon and pyroclastic beds ), constituting approximately 6 km wide zone along the eastern border of Dharwar belt. It has been evidenced that there is a presence of platinum mineralization in the Usgao layered ultramafic complex andmolybdenum mineralization associated with aplite-pegmatite phase of Ramnagar Migmatite, about 12 km from Kumbarwada. Vestiges of 2.9 Ga old event forming a part of Chandranath Granite and Ramnagar Migmatite have been recognized based on preliminary Sm-Nd isotope analysis.

Palaeomagnetism and Geochemistry of the mafic dyke swarms of Proterozoic Cuddapah and other sedimentary basins of South India.

Under the above mentioned project it has been reported that the Rb-Sr and Sm-Nd isotopic data suggesting Palaeoproterozoic ( c. 2200 Ma) ages for the Mahabubnagar dykes has attached great significance for the study as no pole data are available for India for this early period.

Four different magmatic phases with distinct ChRM directions in fifteen sites (dykes) from this area (Mahabubnagar-Wanaparti sector) have been identified. Geochemical data show that the dykes all around the Cuddapah basin are uniform in their tholeiitic composition and the variations can be explained by variable degrees of fractionation of ferromagnesian mineral phases (ol+cpx+pl). The dykes are enriched in LIL (Rb ,Ba ,K) elemental abundances over the HFSE(Zr,Ti,Y,Nb) elements with very conspicuous Nb depletion. Further petrogenic analyses are in progress to evaluate the crustal effects and the nature of mantle sources.

The distinct palaeomagnetic directions do not strictly correlate with any particular field orientation of the dykes. Only exception is in the Mahbubnagar-Wanaparti sector where the sites from all N-S dykes posses steep Ch RM. Otherwise ChRM of dykes of different field orientations show undisputed between site grouping. Thus the notion that dykes with different field orientations belong to distinct magmatic phases does not appear to be tenable.

Global Optimization of gravity anomaly using Genetic Algorithm

Genetic Algorithm has been used to interpret gravity anomaly over a sedimentary basin. It has been found that incorporating information of the gradients of the observed gravity anomaly improves the fitness between the observed and calculated anomalies. Use of pseudo subspace method to increase the complexity in the basement structure improves the performance of the proposed method significantly as demonstrated by analyzing a simulated case and a real example from Jharia coal field.

Completed Projects

Tectonics of the eastern sector of the Palaghat-Cauvery lineament.

The granulite facies mineral assemblages and the presence of granoblastic textures in large parts of the area indicate that no major shear zone passes through the area. The fold pattern in the Namakkal region does not fit with the interpretation of dextral shear as interpreted by many workers earlier. The fold pattern is suggestive of shortening across the zone rather than simple transcurrent motion. No mylonite belt separates the granulite and amphibolite facies terranes, and therefore, the structural, textural features do not support the interpretation that the two terranes are brought into juxtaposition by a major transcurrent motion.

Geochemistry of Mineralizing fluids in the Hutti Gold deposit, Raichur,
Karnataka.

Under the above mentioned completed project, it has been reported that Gold mineralisation at Hutti is localized along nine well defined parallel to sub parallel narrow zones of highly sheared chlorite-biotite-carbonate schists with quartz veins. Gold occurs in native form as minute globules, specks, thin stringers, films and smears along the fractures within quartz. It also occurs associated with scheelite and sulphide minerals such as arsenopyrite,pyrrhotite, pyrite, chalcopyrite and sphalerite in the altered wall rocks that occur as lenses within the quartz vein or on either side of it. At least five major types of fluid inclusions were recognized in the quartz prophyroblasts with a fairly wide range of components. This diversity can be explained as due to changes in physical and chemical conditions that affect a low salinity fluid during the dynamic evolution of shear zone. The carbon isotope studies indicate that the carbon derived from deep crustal sources and hence the fluid that is added to the plumbing system in the shear zone is inferred to be of deep crustal origin. It is inferred that nteraction
of deep crustal fluids with basaltic flows in the greenstone belt may result in leaching of gold and other metals into the fluid system.

Publication

With a view to disseminate information regarding achievements of the Projects under implementation and other issues related to the DCS Programme, DCS Newsletter is being brought out. 2 issues of the DCS Newsletter have been brought out during the current year.